package com.zhouwr.common.utils;

public class CRCUtil {
  /**
   * 计算CRC16校验码
   *
   * @param data 需要校验的字符串
   * @return 校验码
   */
  public static String getCRC(String data) {
    data = data.replace(" ", "");
    int len = data.length();
    if (!(len % 2 == 0)) {
      return "0000";
    }
    int num = len / 2;
    byte[] para = new byte[num];
    for (int i = 0; i < num; i++) {
      int value = Integer.valueOf(data.substring(i * 2, 2 * (i + 1)), 16);
      para[i] = (byte) value;
    }
    return getCRC(para);
  }

  /**
   * 计算CRC16校验码
   *
   * @param bytes 字节数组
   * @return {@link String} 校验码
   * @since 1.0
   */
  public static String getCRC(byte[] bytes) {
    // CRC寄存器全为1
    int CRC = 0x0000ffff;
    // 多项式校验值
    int POLYNOMIAL = 0x0000a001;
    int i, j;
    for (i = 0; i < bytes.length; i++) {
      CRC ^= ((int) bytes[i] & 0x000000ff);
      for (j = 0; j < 8; j++) {
        if ((CRC & 0x00000001) != 0) {
          CRC >>= 1;
          CRC ^= POLYNOMIAL;
        } else {
          CRC >>= 1;
        }
      }
    }
    // 结果转换为16进制
    String result = Integer.toHexString(CRC).toUpperCase();
    if (result.length() != 4) {
      StringBuffer sb = new StringBuffer("0000");
      result = sb.replace(4 - result.length(), 4, result).toString();
    }
    // 交换高低位
    return result.substring(2, 4) + result.substring(0, 2);
  }

  public static void main(String[] args) {
    System.out.println(getCRC("03 04 04 01 09 01 7c")); // 09 CB
  }
}
